Structural articles with load bearing capabilities

ABSTRACT

A method of forming a structural article from a shape defining interior member ( 20 ) and at least one external skin ( 22 ). The interior member has at least one surface ( 23 ) with channels extending to the periphery thereof. The method comprises heating a thermoplastics sheet intended to form said external skin ( 22 ) and bringing the heated sheet ( 22 ) alongside the surface ( 23 ) of the interior member ( 20 ) and into initial contact with same. A fluid pressure differential is then applied between opposite surfaces of the interior member ( 20 ) and the sheet ( 22 ) to conform the sheet ( 22 ) to the shape of the interior member ( 20 ) and mutually engage same. Fluid trapped between the sheet ( 22 ) and the member ( 20 ) escapes through the ends of the channels of the member ( 20 ) as the sheet ( 22 ) is drawn into substantially conformity with the surface ( 23 ) having the channels. The fluid pressure differential is maintained until the sheet ( 22 ) has cooled whereupon tensional forces arise in the sheet ( 22 ) in all directions. Articles having load bearing capabilities formed by the above method are also disclosed.

FIELD OF THE INVENTION

The present invention relates to an improved method for forming astructural article from a shape defining interior member and at leastone external skin. The invention also relates to the articles formed bythe improved method.

BACKGROUND OF THE INVENTION

A method and apparatus for forming structural articles (known as theARMACEL process), and articles so formed, is disclosed in theapplicant's international PCT patent application No. PCT/AU95/00100entitled “A method and apparatus for forming structural articles” (WO95/23682) and international PCT patent application No. PCT/AU96/00541entitled “Layered Structural Article” (WO 97/09166).

These applications disclose forming structural articles from a shapedefining interior member and at least one external skin in which theinterior member is at least partially fluid permeable. The basic stepsof the method comprise: (1) heating a thermoplastics sheet intended toform the external skin; (2) bringing the heated sheet alongside theinterior member; (3) applying a fluid pressure differential betweenopposite surfaces of the interior member and the sheet to conform thesheet to the shape of the interior member and mutually engage same; and(4) maintaining the fluid pressure differential until the sheet hascooled. At the commencement of step (3), the headed sheet forms a sealaround the periphery of the interior member which traps air between theadjacent surfaces of the sheet and the interior member. During step (3),the air trapped between the sheet and the interior member is removed bybeing drawn through the (at least partially fluid permeable) interiormember by the pressure differential.

This method requires the interior member to inherently be at leastpartially fluid permeable or to be modified so as to be at leastpartially fluid permeable, for example by punching holes into themember. Further, fluid permeability in one direction is lost when a skinis applied to one side of the member and holes must be then placed inthat skin in order to allow the application of another skin to the otherside of the member.

It is an object of the present invention to provide an improved methodin which the shape defining interior member does not necessarily have tobe at least partially fluid permeable.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is discloseda method of forming a structural article from a shape defining interiormember and at least one external skin, said interior member having atleast one surface with channels extending to the periphery thereof, saidmethod comprising the steps of:

(1) heating a thermoplastics sheet intended to form said external skin;

(2) bringing the heated sheet alongside the surface of said interiormember having said channels and into initial contact with same;

(3) applying a fluid pressure differential between opposite surfaces ofsaid interior member and said sheet to conform said sheet to the shapeof said interior member and mutually engage same, fluid trapped betweensaid sheet and said member escaping therefrom through the channels atthe periphery of said interior member as said sheet is drawn intosubstantial conformity with the surface having said channels; and

(4) maintaining said fluid pressure differential until said sheet hascooled whereupon tensional forces arise in said sheet in all directions.

If desired more than one surface of the interior member can havechannels and be covered with a corresponding skin. The fluid ispreferably a gas rather than a liquid and most preferably air.

According to a second aspect of the present invention there is disclosedan article having load bearing capabilities, said article comprising ashape defining interior member and at least one external skin, saidinterior member having at least one surface with channels extending tothe periphery thereof, said skin being a thermoplastic sheet, whereinsaid sheet is softened by heating and substantially conformed to theshape of the surface of said interior member having the channels byapplying a fluid pressure differential therebetween which removes fluidtrapped between the sheet and the member through the channels at theperiphery of the surface having the channels, said fluid pressuredifferential being maintained until said sheet has cooled wherebytensional forces arise in said sheet in all directions.

The channels can be uniform or non-uniform, parallel or non-parallel, ofthe same size or of different sizes.

The channels can also include small grooves in their deepest regions tofurther aid in fluid removal.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexamples only, with reference to the accompanying drawings in which:

FIG. 1 is a side view of an interior member and skin at the beginning ofa forming method according to a first embodiment of the invention;

FIG. 2 is a side view of the interior member and skin shown in FIG. 1midway through the forming method;

FIG. 3 is a side view of the interior member and skin shown in FIG. 1 atthe completion of the forming method;

FIG. 4 is an enlarged detail view of a portion of the interior memberand skin shown in FIG. 3;

FIG. 5 is a side view of another interior member and skin at thecompletion of the forming method according to the invention; and

FIGS. 6 through 12 are each perspective views of various articles formedin accordance with the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the method according to the present invention willnow be described with reference to FIGS. 1 to 4. An apparatus suitablefor performing this method is disclosed in the applicant's twointernational PCT patent application referred to earlier, the relevantdisclosure of each of those specifications being incorporated herein bycross reference.

FIG. 1 shows a shape defining interior member 20 and an external skin22. The upper surface 23 of the member 20 has channels formed by regularsequential peaks 24 and troughs 26. The peaks 24 and troughs 26 of theinterior member 20 can be produced from a variety of materials. Apreferred form of interior member 20 is produced by removing one layerfrom conventional cardboard which is traditionally formed from a firstouter planar layer, an inner corrugated layer and a second outer planarlayer. Alternatively, the interior member 20 can be formed by removingincomplete cardboard from the manufacturing process before applicationof the second outer planar layer to the corrugated layer. In addition tothe cardboard type structures shown, channels can be added to a surfaceof other materials by many means including machining, rolling, notching,scoring and the like.

In the method of the present invention, the external skin 22 is formedfrom a thermoplastics sheet which is soften by heating and brought alongside the upper surface 23 of the interior member 20 and into contactwith the peaks 24 of same. A fluid pressure differential is applied,preferably by creating a vacuum by air removal, between oppositesurfaces of the interior member 20 and the skin 22 to substantiallyconform the sheet 22 to the upper surface 23 of the interior member 20and mutually engage same. As FIG. 1 shows, the sheet 22 initiallybridges the peaks 24 and the air trapped between the sheet 22 and theupper surface 23 of the member 20 is able to escape through the ends ofthe troughs 26 at the periphery of the interior member 20. As the fluidpressure differential sucks the trapped air away, the portion of thesheet 22 bridging the peaks 24 begins to be drawn down into the troughs26, as shown in FIG. 2. When nearly all of the trapped air has beenremoved the sheet 22 is substantially conformed to the shape of theupper surface 23. When the sheet 22 has cooled the fluid pressuredifferential can be removed and the finished structural article removedfrom the apparatus (not shown).

As shown in FIG. 4, the above described method may not remove all of thetrapped air and a small amount of the skin 22 may not confirm to theupper surface 23, as indicated by region 28 at the bottom of the trough26.

FIG. 5 shows another interior member 20 which includes small grooves 30at the bottom of the troughs 26 to reduce the size of the non-conformedregions 28. In the embodiment shown in FIG. 5, the majority of thetrapped air is initially removed through the ends of the troughs 26 anda final minority portion is removed through the ends of the grooves 30.

The primary advantage of the present invention is that it allows theARMACEL process to function without necessitating the use of at leastpartially fluid permeable interior members or the application of holesto non-fluid permeable interior members or interior members that havepreviously had one or more surfaces covered by the thermoplastic sheet.

This greatly increases the materials available for use with the ARMACELprocess and, importantly, extends the ARMACEL process for use with, forexample, plastics, timbers and metals.

Another advantage is the improved strength of the finished article inthe longitudinal direction of the channels. In particular, the bondsbetween the interior member and the sheet at the sides of the channelsare more resistant to failure than the bonds between planar surfaces asthe bonds of the side surfaces are better able to resist the stressesapplied thereto in the shear direction than the planar surfaces canresist the stresses applied thereto in the peel direction.

Strength in directions other than the longitudinal can be improved byadding channels to an opposed side of the article that are arranged atan angle to those of the first side. For rectangular articles an angleof 90 degrees between the channels on either side of the article ispreferred.

Applying channels on only one side of an article can also be useful instrengthening the article in the longitudinal direction of the channelswhilst leaving flexibility in a direction normal to the longitudinaldirection. Such flexibility can, for example, be useful in formingcurved articles. Alternatively, the channels can be arranged in morethan one direction on one or more surfaces of the article which areencapsulated by the thermoplastic sheet.

A further advantage is the small portion of the sheet not adhered to theinterior member at the bottom of the troughs is able to expand slightlywhen heated so as to reduce warping in articles that have a hotter and acooler side, such as garage doors.

Additionally, as the method can be used with fluid impermeable interiormembers, it also allows application of a further thermoplastic sheet orsheets to an article on which the ARMACEL process has already beencarried out to thus further improve its strength.

A surface having channels also adds a non-slip capability to thefinished article.

FIGS. 6 through 12 shows various articles formed in accordance with theabove described method.

In particular, FIG. 6 shows a relatively thick article produced byadding the cardboard based structural member 20 shown in FIGS. 1 to 3 toa larger foam base 32 and thereafter applying the thermoplastics skin 22to the corrugated upper surface and sides of the interior member 20 inaccordance with the above described method.

FIG. 7 shows an article formed by placing two of the interior members 20shown in FIG. 1 back-to-back and then sequentially bonding onecorrugated surface then the other. Since the trapped air is removedthrough the ends of the troughs 26, no additional treatment of thesecond side of the article (eg. punching holes) is required beforeapplying the second thermoplastic sheet 22.

FIG. 8 shows a similar article to that shown FIG. 7 except thecorrugations are provided on either side of a single interior member 34and the sides are then sequentially encapsulated with the thermoplasticsheet 22.

FIG. 9 shows a fork lift pallet 36 having a top to which a corrugatedsurface has been applied and then encapsulated with the thermoplasticsheet 22 to improve its strength and grip characteristics.

FIG. 10 shows a wall or furniture panel 38 in which a decorative finishhas been produced by arranging corrugated surfaces 42 at differentorientations over a surface of the panel before encapsulating with thethermoplastic sheet.

FIG. 11 shows an article 44 having an upper surface 45 with randomlyorientated channels 46 therein. The channels 46 can be produced byscoring the surface 45 by coarse sandpaper, a kitchen scourer or sharpimplement such as a knife. The channels 46 are too small for thethermoplastic sheet to be drawn into them and thus function similar tothe grooves 30 shown in FIG. 5 in that a bridge of thermoplastic sheetforms across them. Further, in this embodiment, the channels 46 alsoextend down the sides of the interior member to further improve airevacuation.

FIG. 12 shows a timber decking slat 48 with longitudinal channels 50encapsulated by a thermoplastic sheet 52.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art that theinvention may be embodied many other forms.

1. An article having load bearing capabilities, said article comprisinga shape defining an interior member and at least one external skin, saidinterior member having at least one surface with channels extending tothe periphery thereof, said channels including small grooves in theirdeepest regions, and said skin being a thermoplastic sheet, wherein saidsheet is softened by heating and substantially conformed to a shape ofthe surface of said interior member having the channels by applying afluid pressure differential therebetween which removes fluid trappedbetween the sheet and the member through the channels at the peripheryof the surface having the channels, said fluid pressure differentialbeing maintained until said sheet has cooled whereby tensional forcesarise in said sheet in all directions.
 2. An article having load bearingcapabilities, said article comprising a shape defining an interiormember, at least one side surface extending from the periphery of saidinterior member, and at least one external skin, said interior memberhaving at least one surface with channels extending into said sidesurface, said channels including small grooves in their deepest regions,and said skin being a thermoplastic sheet, wherein said sheet issoftened by heating and substantially conformed to a shape of thesurface of said interior member having the channels by applying a fluidpressure differential therebetween which removes fluid trapped betweenthe sheet and the member through the channels at the periphery of thesurface having the channels, said fluid pressure differential beingmaintained until said sheet has cooled whereby tensional forces arise insaid sheet in all directions.
 3. The article as claimed in claim 2,wherein the article includes at least one side surface extending fromthe interior member periphery and said channels extend into said sidesurface.
 4. The article as claimed in claim 2, wherein the channels areuniform.
 5. The article as claimed in claim 2, wherein the channels arenon-uniform.
 6. The article as claimed in claim 2, wherein the channelsare parallel.
 7. The article as claimed in claim 2, wherein the channelsare of the same size.
 8. The article as claimed in claim 2, wherein thechannels are non-parallel.
 9. The article as claimed in claim 2, whereinthe channels are of different sizes.
 10. The article as claimed in claim1, wherein the article includes at least one side surface extending fromthe interior member periphery and said channels extend into said sidesurface.
 11. The article as claimed in claim 1, wherein the channels areuniform.
 12. The article as claimed in claim 1, wherein the channels arenon-uniform.
 13. The article as claimed in claim 1, wherein the channelsare parallel.
 14. The article as claimed in claim 1, wherein thechannels are of the same size.
 15. The article as claimed in claim 1,wherein the channels are non-parallel.
 16. The article as claimed inclaim 1, wherein the channels are non-parallel.